This invention relates to a tilt cylinder arrangement for an outboard drive and more particularly to an improved hydraulic tilt control mechanism.
It is well known in marine outboard drives to provide a hydraulic cylinder assembly interposed between the outboard drive portion and the transom of the watercraft for controlling the position of the outboard drive. These mechanisms may also provide a shock absorbing function so as to permit the outboard drive to pop up when an underwater obstacle is struck and then return to its normal position once the underwater obstacle is cleared. A wide variety of hydraulic arrangements have been proposed for this purpose.
Substantially all of these hydraulic arrangements include a double acting hydraulic cylinder assembly wherein flow passes from one side of a piston to the other upon movement and then may return upon return movement. With such arrangements, however, a piston rod is connected to the piston and extends through one of the chambers. Hence, when fluid is interchanged between the chambers, there will be an unequal amount of fluid displacement due to the fact that the piston rod displaces some of the fluid area in the chamber through which it extends. Therefore, it has been practiced to provide some form of makeup chamber which communicates with the device so as to accommodate these changes in fluid displacement caused by the piston rod. Of course, such a makeup device must provide a volume above the fluid so as to accommodate the variations in amount of fluid contained within the makeup chamber. This type of construction gives rise to a number of problems.
Specifically, if the makeup chamber is an open chamber and the gas or air above the fluid is not sealed from the fluid, there is a risk that the gas may enter the hydraulic system and interfere with its effective operation. That is, the air or gas may become entrained in the hydraulic fluid and adversely effect the operation of the fluid device.
Although these problems can be avoided by providing an impermeable barrier between the fluid and the gas or air over the fluid, such an arrangement can add to the cost of the system.
It is, therefore, a principal object of this invention to provide an improved hydraulic cylinder assembly for a marine outboard drive which does not require flow between two chambers of the hydraulic cylinder for its operation.
In systems embodying hydraulic cylinders of the type previously described, it has also been proposed to provide a bypass passageway between the two chambers in which a control valve is positioned. The control valve is opened so as to permit tilting up of the outboard drive without having to overcome the fluid resistance. In addition, it has been proposed to pressurize the gas over the fluid in the system so that the pressure of the gas will assist in raising the outboard drive when the valve is opened. However, the amount of lift provided by the gas pressure is relatively small since the pressure acts only over the differential area established by the piston rod. That is, it is not possible to provide separate pressurization which can act to assist in lifting the outboard motor since both chambers normally communicate with each other.
It is, therefore, a further object of this invention to provide an improved hydraulic arrangement for an outboard drive wherein the system can be pressurized to provide adequate lift without having it upset the normal operation of the outboard drive.
It is a further object of this invention to provide an improved hydraulic control for a marine outboard drive.
In addition to the difficulties as aforenoted, the types of hydraulic devices previously described also have the problem in that each chamber of the fluid cylinder must be filled with the same fluid due to the interchange of fluid between the chambers. Because of this, it is not possible to employ different fluids so as to provide different types of effects.
It is, therefore, a still further object of this invention to provide an improved hydraulic assembly for a marine outboard drive that can be double acting and which still may employ different fluids in each chamber.